P807: CLASS Ⅱ FERROPTOSIS INDUCERS ARE A NOVEL THERAPEUTIC APPROACH FOR T(4;14)-POSITIVE MULTIPLE MYELOMA
Authors: Jiasi Zhang, Yuxi Liu, Liping Zuo, Fengjuan Fan, Han Yan, Fei Zhao, Bo Zhang, Yu Hu, Chunyan Sun
Journal: HemaSphere (2023)

Topic: 13. Myeloma and other monoclonal gammopathies - Biology & Translational Research Background: Multiple myeloma (MM) is characterized by genetic heterogeneity. The cytogenetic abnormality t(4;14) strongly predicts poor outcomes in MM patients. MM SET domain-containing protein (MMSET) is overexpressed in t(4;14)-positive MM and contributes to tumor progression. But the development of targeting MMSET by small molecule inhibitors seems challenging and its effectiveness remains to be verified. Ferroptosis is a non-apoptotic form of cell death. Inducing ferroptosis strengthens the efficacy of existing treatments, even drug-tolerant tumor cells are vulnerable to ferroptosis, implying a potent anti-tumor activity of ferroptosis inducers (FINs). However, the prediction of ferroptosis sensitivity remains debated. In particular, studies of ferroptosis in MM remains largely unknown. Aims: To investigate ferroptosis sensitivity in t(4;14)-positive MM and its underlying mechanism. Methods: First, we analyzed enrichment pathways in MMSET-related public datasets. The effect of chromosome t(4;14) status or MMSET expression on MM ferroptosis sensitivity was detected by CCK-8, RT-qPCR, flow cytometry, and electron microscopy. Then we performed the correlation analysis between MMSET and long-chain acyl-CoA synthetase 4 (ACSL4) in MM cell lines and primary MM cells by bioinformatics, western blotting, and immunohistochemistry. The regulation of MMSET on ACSL4 expression and the role of MMSET/ACSL4 axis on MM ferroptosis sensitivity was investigated in vitro and in vivo. Next, the effect of fatty acids supplementation on MM ferroptosis sensitivity was detected. Metabolomics was applied to study the impact of ACSL4 on fatty acid composition in MM. Additionally, the curative effect of FINs and bortezomib on MM was evaluated in vitro and in vivo. Ferroptosis-associated proteins and intracellular glutathione levels were detected in MM treated with bortezomib/FINs alone or together. Results: Both ferroptosis and polyunsaturated fatty acids (PUFAs) synthesis pathways are enriched in MMSET-related public datasets. MM cell lines or primary MM cells with t(4;14)-positive are more vulnerable to class II FINs compared to t(4;14)-negative, while little damage is observed by FINs in normal cells. Knockdown of MMSET renders t(4;14)-positive MM remarked resistance to ferroptosis. Mechanistically, MMSET upregulates ACSL4 transcription by binding to its promoter, leading to increased levels of PUFAs and enhanced sensitivity of t(4;14)-positive MM to ferroptosis. Indeed, ACSL4 increases multiple PUFAs including adrenal acid (AdA) levels and promotes sensitivity of t(4;14)-positive MM to ferroptosis. Supplementation of PUFAs restores ferroptosis susceptibility of t(4;14)-negative MM or t(4;14)-positive MM with MMSET or ACSL4 knockdown. Moreover, bortezomib upregulates the expression of ferroptosis-associated protein xCT in MM, independent of t(4;14) status. Co-treatment with class II FINs abrogates the upregulation of xCT by bortezomib in t(4;14)-positive MM, but not t(4;14)-negative MM. Combination therapy attenuates cellular glutathione levels and triggers both apoptosis and ferroptosis in t(4;14)-positive MM, displaying a synergistic anti-tumor activity in vitro and in vivo. Summary/Conclusion: We report the vulnerability of t(4;14)-positive MM to ferroptosis and suggest class II FINs as a novel therapeutic approach for t(4;14)-positive MM, particularly in combination with bortezomib.Figure 1. Class II ferroptosis inducers are a novel therapeutic approach for t(4;14)-positive multiple myeloma Keywords: Multiple myeloma